The inventory supplies is up to an option *no tax or *gst (which you have to setup in your system) as for the total zero rated supply, it is enough as putting the code in front before your item code. As the example for Zero Rated Supply (ZRL-FLOUR) … things sort to be like that…
You may refer to the linked below for GST CODES
http://www.1gst.com.my/gst-library/115-gst-tax-codes.html
OR you can refer to this guideline Setting up tax codes